Neurotropic herpesviruses are important pathogens causing serious diseases in humans and animals. These viruses have the capacity to infect the central nervous system (CNS) and other tissues to produce lytic infection, after which they establish a reactivatable latent infection in the peripheral ganglia. The long term goal of this project is to understand in molecular details the mechanisms used by neurotropic herpesviruses to invade and cause disease in the mammalian nervous system. Understanding these mechanisms may lead to the development of better prophylactic and curative treatments that block viral neuropathogenesis. Bovine herpes virus type 1 (BHV-1) and type 5 (BHV-5) are economically important neurotropic alpha-herpesviruses that cause disease in cattle and share structural, genetic, and biological similarity to the human herpes simplex virus (HSV) types 1 and 2 and swine pseudorabies virus (PRV). While BHV-1 and BHV-5 are neurotropic and share high DNA homology, only BHV-5 causes distinct neurological disease. Our specific aim is to use BHV-1/BHV-5 as a model to study the role of viral glycoproteins in neuropathogenesis. Several viral genes have been suggested to be involved in neuropathogenesis among herpesviruses. However, the specific role of the envelope glycoprotein genes in neuroinvasiveness and neurovirulence is still largely unknown. Preliminary data showed differences in glycoprotein C (gC) and glycoprotein (gD) at the molecular structural and antigenic levels between the two viruses. As with other alpha herpesviruses, glycoprotein B (gB) appears to be highly conserved. We hypothesize that the differences of these glycoproteins and probably others between the two viruses have critical functional significance in viral neuropathogenesis. To test this hypothesis, our approach centers on the genetic and functional analysis of the glycoprotein genes of the two viruses. In specific aim 1, we will further compare and analyze the molecular and antigenic structures of BHV-1 and BHV-5 gC, gD, and gB to explore for regions of potential functional significance. In specific aim 2 and 3 we will construct and characterize BHV-1 and BHV-5 virions lacking a specific glycoprotein coding genes to directly examine the role of these glycoproteins in neurological disease. This will be achieved in specific aim 4 by evaluating the neuropathogenic properties in vitro in neuron cell culture and in vivo in a rabbit model. Analysis of results will determine if the genetic deletions will alter the neuropathogenic potential of the viruses and whether or not this alteration is due to a defect in one or more of the virus infective properties to some or all functional regions of the CNS. The proposed experiments will provide a clear genetic definition for the functional role of these glycoproteins and undoubtedly will give significant insight into the molecular mechanisms of neurological disease caused by many alpha-herpesviruses.